1. Field of Invention
The present invention relates to grinding machines and more particularly to a screw based mechanism for fine tilting adjustment of a spindle unit prior to operating the spindle unit to grind a semiconductor wafer to a predetermined thickness.
2. Related Art
The minimum encapsulation size of a semiconductor wafer produced in a manufacturing process is decided by thinning. Surface roughness, thickness variance, and performance are important factors in the thinning process. In a first half of the thinning process, devices formed on the wafer are separated by dicing (i.e., sawing). For eliminating traces left by sawing, grinding is performed on the wafer for making the wafer having a surface flatness sufficient for a subsequent polishing process. For an 8″ wafer, its total thickness variance (TTV) is required to be equal to or less than 5 μm.
For example, a grinding machine shown in FIG. 1 is disclosed in U.S. Pat. No. 6,685,542 in which two rotary screw rods (one is shown) 51 are laid on an upright wall 50, two spindle units 52 (one is shown) each is adapted to raise or lower by rotating the rotary screw rod 51, a grinding wheel 53 is attached to a lower surface of either spindle unit 52, the grinding wheel 53 having segments of fine or coarse grindstone 54, three chuck tables (one is shown) 55 are rotatably fixed to a turntable, and two adjustment screws 56 are provided below each chuck table (e.g., chuck table 55). The adjustment screws 56 are adapted to turn to adjust the tilting angle of the chuck table 55 for being adapted to the angle of an approaching cutter in the grinding.
However, the first prior art suffered from several disadvantages. For example, it is relatively complex in constructions due to the provisions of two adjustment screws 56 below each chuck table 55 and other associated taking and putting equipment and transporting means. Moreover, the chuck tables 55 are adjustable, resulting in a decrease of its supporting capability (i.e., less stiff). In brief, the tilting adjustment mechanism is not desirable.
In another example a grinding machine shown in FIG. 2 is disclosed in Japanese Patent Laid-Open No. 11-309,673 in which a carrier 61 is slidably mounted on an upright wall 60, a pivot axis 62 is interconnected the carrier 61 and a forward block member 63, a wedge member 65 is provided at an upper part of the block member 63, a rotary screw rod 64 has a lower end threadedly engaged with the wedge member 65, a spindle unit 66 is threadedly engaged with a front portion of the wedge member 65 by means of upper and lower screws 67, an upper ball 69 is provided in an upper V-shaped groove 68 of the spindle unit 66 to be in rotatable contact with an inclined surface of the wedge member 65, and a lower ball is provided in a lower V-shaped groove of the spindle unit 66 to be in rotatable contact with the block member 63. For tilting the spindle unit 66, first unfasten the screws 67, and then rotate the rotary screw rod 64 to raise or lower the wedge member 65. As a result, either the spindle unit 66 tilts clockwise if the wedge member 65 raises or the spindle unit 66 tilts counterclockwise if the wedge member 65 lowers. This is the tilting adjustment operation of the spindle unit 66.
Referring to FIG. 3, a U-shaped mount 70 is provided on a top of the carrier 61 and above the block member 63 by a small distance. A pressing member 72 is provided in the recess of the U-shaped mount 70. A rotary screw rod 71 is threadedly engaged between the pressing member 72 and one lateral portion of the mount 70 such that the pressing member 72 may move by rotating the rotary screw rod 71. The center of gravity of the block member 63 changes in response to the movement of the pressing member 72. And in turn, the block member 63 pivots about the pivot axis 62. This is the tilting adjustment operation of the block member 63.
However, the second prior art suffered from several disadvantages. For example, weights of both the block member 63 and the spindle unit 66 concentrate on the pivot axis 62, resulting in a breaking of the pivot axis 62 (i.e., useful life shortened). Further, the block member 63 is not able to maintain the angle of being tilted due to no positioning device associated therewith. This is not desired in the grinding operation. Thus, the need for improvement still exists.